Introduction: One of the side effects of myocardial infarction(MI) is a change in slow contraction muscle phenotype to fast contraction due to decreased mitochondrial density. Mitochondrial biogenesis with its ability to create new mitochondria and increase mitochondrial density can minimize these complications. Therefore, the aim of this study was to investigate the effect of eight weeks of high intensity interval training on peroxisome-proliferator activated receptor γ coactivator (PGC-1α) gene expression levels in fast twitch (FT) and slow twitch muscle (ST)  muscles in rats with myocardial infarction.
Materials and methods: For this purpose, 12 Wistar male rats with MI were divided into two experimental groups (30 minutes on a treadmill on a regular basis and 4 minutes running with a severity of 85-90% VO₂ max and two minutes of active recovery with 50% -60% VO₂max three days a week for eight weeks) and control (without exercise). The expression of PGC-1α genes was studied as an effective factor in mitochondrial biogenesis. Statistical data were analyzed with independent T-test in SPSS18.
Results: The results showed that the expression of PGC-1α genes increased significantly in ST (P=0.012) and FT (P=0.001) muscles in rats with MI. Also, this increasing in the ST muscles was significantly higher than those in the FT muscles (P=0.000).
Conclusion:  Generally, eight weeks of high intensity interval training increase mitochondrial biogenesis in ST and FT muscles of MI rats through effect on the PGC-1α gene expression.